Ear shield and acoustic transmitting device



W 1944- E. s. PRIDHAM EAR SHIELD AND ACOUSTIC TRANSMITTING DEVICE Filed NOV. 24, 1941 IINYVENTOR.

III m 11 h Patented Feb. 15, 1944 EAR SHIELD AND ACOUSTIC TRANSMITTING DEVICE Edwin S. Pridham, Fort Wayne, 1nd,, asslgnor, by mesne assignments, to The Magnavox Company, Fort Wayne, Ind., a corporation of Delaware Application November 24, 1941, Serial No. 420,219

5 Claims.

This invention relates to acoustic transmitting devices for use in the presence of strong extraneous sound waves, and more especially to devices for protecting the eardrums from sound waves caused by strong concussions while at the same time permitting desired sound waves to be eflective on the ear-drum.

It is a well known fact that, in positions of heavy gun-fire such as turrets, tanks and any other place where there are more or less incessant strong vibrations, the ear-drums of persons subjected to such vibrations are adversely affected. In severe cases the ear-drum may be ruptured.

The usual method of protecting the ear-drum is to plug the ear with cotton. This gives only partial relief since a great deal of sound is transmitted to the ear-drum through the bones around the ear. Moreover, if the ear canal is tightly plugged with cotton it is practically impossible to convey audible messages.

The object of the present invention is to protect the ear-drum from heavy concussive vibrations, while at the same time permitting wanted audible vibrations to produce their full effect to transmit communications.

In the present invention use is made of a diaphragm openly exposed on both sides to extraneous sound vibrations for the purpose of holding to an ear-drum protector combined with an acoustic transmitter for transmitting wanted audible signals to the ear canal, while effectively blocking out the unwanted or extraneous noises, certain new and useful improvements have been made as will hereinafter appear.

In making use of the balanced diaphragm principle for an ear-drum protector and acoustic transmitter it is necessary to combine in a casing,

a diaphragm couple. This couple generally consists of a receiving diaphragm located, to be openly exposed on both of its sides, in the outer part of the casing, and a sound producing diaphragm located in the inner part of the casing and protected from the eilects of extraneous noise. These two diaphragms are connected together by a rigid driving member whereby move: ments of the receiving diaphragm due to wanted voice vibrations are transmitted to the sound producing diaphragm. The sound reproducing diaphragm is located in a chamber of the casing and is protected by a plug of sound-excluding material located in the casing between the two diaphragms. The inner end of the casing is formed in the shape of a tube forming a continuation of the protected diaphragm chamber.

In practice this casing, with its openly exposed diaphragm and its protected diaphragm, and its chamber with its ear tube, is held in a shield of soft absorbent material so formed as to cover the ear and form a cushion over the bones directly behind the ear so as to prevent shock vibration to these bones.

It is necessary that the ear is thoroughly protected from vibrations except those which can enter through the anti-noise diaphragm. One method of holding the earshields or protectors closely against the ears is to have a strap or adjustable head band attached to the shields by means of a pressure plate, and an elastic web to fit under the chin. In this manner the shield with its aural tube can be positioned securely to direct the wanted vibrations into the ear canal and at the same time hold the shield closely over the ear and in contact with the bones surrounding the ear.

Further objects of the invention will become apparent from the following description of the device which is given by way of example only, it being understood that any modification within the scope of the invention may be utilized without departing from the spirit thereof.

In the drawing:

Fig. l is'a schematic cross sectional view of a diaphragm couple and its casing according to the present invention.

Fig. 2 shows, in cross section, a further embodiment of a diaphragm assembly according to the invention.

Fig. 3 is a plan view of the assembly of Fig. 2.

Fig. 4 is a central vertical section showing the diaphragm couple of Figs. 2 and 3 and its casing embodied in an ear-drum protector, all

according to this invention.

Referring to the drawing, Fi 1 illustrates the principles of the diaphragm-couple utilized in accordance with the invention. The sound-producing diaphragm 2 is mounted within a plug 4 preferably of moulded soft rubber and having the shape of a truncated cone. The diaphragm 2 is placed a short distance from the inner end of the plug 4, which forms an aural tube, so as to provide a chamber 6 between it and said inner end to provide a space within which the diaphragm can work.

The diaphragm 2 is connected by a rod 8 to a. second or sound receiving diaphragm H] which is disposed within a casing 12, preferably of the same material as the plug 4 and either secured to or formed integral with the latter. It will be noted that the diaphragm it! is so mounted within the casing that its Outer surface is exposed to the atmosphere, as is also its inner surface by means of an aperture l6. or a plurality of apertures, with which the casing is provided.

In the operation of the device extraneous sound waves have access to and strike both sides of the diaphragm in with equal or approximately equal intensity, while the voice waves strike only one side, that is, the outer side of the diaphragm l0. Consequently, if the diaphragm I is balanced for the extraneous vibrations then only the voice vibrations are effective thereon and these only are passed on, by movement of the rigid driving member 8 to the diaphragm 2.

While Fig. 1 shows the principle of operation, I

have found that, in practice, the more the sound producing diaphragm 2 is protected from the direct effects of extraneous sounds the more efficient the device works and hence an arrangement embodying such an improvement is illustrated in Fig. 2. In this figure the diaphragm couple 2-8-41! is mounted in a casing or a frame 43 made up of formed strips it, the bottom of this frame being formed with a ring is for receiving the diaphragm 2 as shown in Fig. 3, and the opposite or upper end of the frame being formed as a second ring 22 to receive and support the diaphragm it). A plug 20 of sound excluding material is fitted Within the frame l3 so as to closely engage the sides thereof. A narrow channel 26 is provided centrally of the plug 20 through which the rod or pin 8 which connects the two diaphragms can pass. is formed to closely fit the rod 8 but not so as to interfere with its free motion. The plug 20 terminates at its upper edge some distance short of the diaphragm IB so that extraneous vibrations admitted through the openings It can be effective on the under side of the said diaphragm, whilst at its lower end the plug 20 is slightly concaved as at 26 to afi'ord space for the vibration of diaphragm 2.

After the assembly of the diaphragms 2 and I ii, the rod 8 and the plug 2b in" the frame I3, the device is housed as shown in Fig. 4 in an ear shield 26 made of a soft sound excluding and absorbing material such as sponge rubber. The

inner part 30 of the shield is formed with an opening 32 so that the shield can be fitted The channel 26 shield can be pressed securely againstath may structure above and just back of the e be noted that the outer portion 36 of th ;shleld is provided with a centrally located opening ,98

to receive the diaphragm assembly, the said opening terminating in the aural tube 46. This to form a covering seat 42 for the diaphragm assembly, the covering being apertured as at 44 and 46 so as to expose both sides of the diaphragm to atmosphere. The outer portion I6 of the shield is provided with a pressure plate ll to which any suitable fastening means may be secured for holding the shield securely against the ear of the wearer. A convenient fastening means is shown in Fig. 5 and consists in an elastic web chin strap 50 connected to the lower ends of a pair of pressure plates 48 mounted on opposed ear shields E and E, an adjustable head strap 52 being connected to the upper ends of said pair of plates 48. Fig. 6 shows the adaptation of the diaphragm assembly to a standard upright telephone set. In this arrangement the casing 52 housing the diaphragm assembly takes a somewhat different shape, more particularly in that it is provided with an extension 54 adapted to fit over the mouthpiece 56 of the telephone set. It will be readily seen that any sounds expressly directed against the diaphragm ID are transmitted to the diaphragm 2 and which sounds in turn will be efiective on the telephone transmitter 58, whilst any extraneous sounds striking both sides of the exposed diaphragm I will be balanced out and are thus inefiective, as will now be clear.

Fig. 7 shows an adaptation of the present diaphragm couple -to the cradle-type telephone set. 60 is the mouthpiece of the transmitter and it will be noted that, in this case, the casing 02 housing the diaphragm assembly, is shaped so as to snugly fit and be held in place by the-said mouthpiece.

While having explained the operation of the present device for use as an acoustical transmitter, I do not wish that a limited interpretation skilled in the art that the principle of this invention can be used effectively for underwater com'- mun'ication where it may be desired. Forsuch purposes the exposed diaphragm is held in static balance by high pressures acting on each side of the diaphragm while wanted vibrations can be transmitted to a diaphragm protected from these high pressures. couple useful for transmission underwater where the protected diaphragm inside the ship's hull initiateslthe signal which is carried to the exposed diaphragm through the connecting rod. Under these circumstances the initiating dia phragm is not subject to any pressure due to the depth of the water while the balanced diaphragm may be so arranged that vibrations transmitted to it are efl'ective for communication.

Having now described the invention,

I claim:

1. In an acoustic transmitting device, a casing, a first diaphragm mounted in a perforated part of the casing permitting free access of sound vibrations to both sides of the diaphragm, a secnnd diaphragm mounted in a sound proof portion of the casing, a rigid member connecting the first and second diaphragms through an opening in said sound proof casing, a chamber in said casing wherein the second diaphragm is free to operate to produce sound waves by virtue of the motion of said member connecting the two diaphragms, and an outlet from said chamber for the sound waves produced by said second diaphragm, for the purposes set forth.

2. In an acoustic transmitting device, a casing, a first diaphragm mounted in a perforated part of the casing permitting free access of sound vi- Especially is such a diaphragm brations to both sides of the diaphragm, a second diaphragm mounted in a sound proof portion of the casing, a rigid member connecting the first and second diaphragms through an opening in said sound proof casing, a chamber in said casing wherein the second diaphragm is free to operate to produce sound waves by virtue of the motion of said member connecting the two diaphragms, an outlet from said chamber for the sound waves produced by said second diaphragm and an extension adapted to fit within the ear of the wearer for the p poses set forth. v

3. In an acoustic transmitting device, a casing, a first diaphragm mounted in a perforated part of the casing permitting free access of sound vibrations to both sides of the diaphragm, a second diaphragm mounted in a sound proof portion of the casing, a rigid member connecting the first and second diaphragms through anopening in said sound proof casin a chamber in said casing wherein the second diaphragm is free to op- 4. In an acoustic transmitting device, a casing, a first diaphragm mounted in a perforated part of the casing permitting free access of sound vibrations to both sides of the diaphra m, a second diaphragm mounted in a sound proof portion of the casing, a rigid member connecting the Y first and seconddiaphragms through an opening in said sound proof casing, a chamber in said casing wherein the second diaphragm is free to operate to produce sound waves by virtue of the motion of said member connecting the two diaphragms, an outlet from said chamber for the sound waves produced by said second diaphragm, and an extension on said casing adapted to fit over the mouthpiece of a standard upright telephone set, for the purposes set forth.

5. An acoustic transmitting device, the combination of a normally sound-balanced diaphragm erate to produce sound waves by virtue of the I the ordinary standard cradle telephone set, for

the purposes setfortb.

subject to equal pressure or sound on both sides,

an unbalanced sound diaphragm subject to pressure or sound on one side only and sound-proofed from'said first diaphragm. a rigid member connecting said diaphragms whereby anunbala'nced pressure or sound imposed upon one diaphragm will be directly transmitted to the other diaphragm, and a chamber for said unbalanced diaphragm having an outlet for the sound waves produced therethrough.

, EDWIN S. PRIDHAM. 

